Conductive porous layer for batteries and fabrication method for same

ABSTRACT

The conductive porous layer for batteries according to the present invention comprises a laminate comprising a first conductive layer and a second conductive layer. The first conductive layer includes at least a conductive carbon material and a polymer. The second conductive layer includes at least a conductive carbon material and a polymer. The conductive porous layer satisfies at least one of the following two conditions: “the polymer in the first conductive layer is present with a high density at the surface of the layer in contact with the second conductive layer than at the surface not in contact with the second conductive layer” and “the polymer in the second conductive layer is present with a higher density at the surface of the layer in contact with the first conductive layer than at the surface not in contact with the first conductive layer.”

This application is the National Stage of PCT International ApplicationNo. PCT/JP2012/057646 on Mar. 23, 2012, which claims the benefit under35 U.S.C. Section 119(a) to Patent Application No. 2011-067654, filed inJapan on Mar. 25, 2011, all of which are hereby expressly incorporatedby reference into the present application.

TECHNICAL FIELD

The present invention relates to a conductive porous layer forbatteries, and a production method thereof. When used for fuel cells,the conductive porous layer for batteries of the present invention canbe used as a gas diffusion layer.

BACKGROUND ART

Electrochemical cells such as fuel cells and metal-air batteries, whichuse gas in an electrode reaction, are provided with a conductive porouslayer to improve the battery performance thereof.

For example, a membrane-electrode assembly (MEA) that is used as acomponent of a solid polymer fuel cell has a structure wherein aconductive porous layer, a catalyst layer, an ion-conductive solidpolymer electrolyte membrane, a catalyst layer, and a conductive porouslayer are sequentially laminated.

Generally, a conductive porous substrate, such as carbon paper or carboncloth, is used for this conductive porous layer. Further, to improve theconductivity, gas diffusivity, water drainability, etc., of theconductive porous substrate, a conductive layer comprising conductivecarbon particles, water-repellent resin, etc., may be formed on theconductive porous substrate.

Conventional conductive porous layers are formed by applying aconductive layer-forming paste composition to a conductive poroussubstrate having a surface roughness of about tens of μm, such as carbonpaper or carbon cloth, and then drying (application methods; see PatentLiterature (PTL) 1 and 2). Therefore, due to the penetration of thepaste composition into the conductive porous substrate surface, etc., itwas difficult to form a conductive layer with a uniform thickness. Whenthe film thickness of the conductive layer is not uniform as describedabove, that is, when there is variation in the film thickness of theconductive layer, stable permeation and diffusion of gas over theadjacent catalyst layer surface is impossible, which lowers fuel cellperformance. Another method for producing a conductive porous layercomprises forming a conductive layer on a transfer film by a transfermethod, then pressure-welding the conductive layer onto the conductiveporous substrate, and removing the transfer film. However, compared tothe above application methods, this method is insufficient in terms ofadhesion between the conductive porous substrate and the conductivelayer. Thus, there is room for improvement in battery performance, etc.The above problem is not limited to solid polymer fuel cells, but isalso common among metal-air batteries, and the like.

CITATION LIST Patent Literature

PTL 1: JP2006-278037A

PTL 2: JP2006-339018A

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide a conductive porouslayer that has good adhesion between the first conductive layer andsecond conductive layer, and that has reduced film thickness variationin each conductive layer.

Solution to Problem

In view of the above problems, the present inventors conducted extensiveresearch to impart the desired properties to a conductive porous layerfor batteries. As a result, the inventors found that a conductive porouslayer for batteries that can solve the above problems can be provided byusing a first conductive layer and a second conductive layer comprisingspecific components. The present invention was accomplished based onthis finding. More specifically, a conductive porous layer thatcomprises a first conductive layer with a stable thickness formed on asecond conductive layer and that has an improved adhesion between thefirst conductive layer and the second conductive layer can be providedby laminating the first conductive layer on the second conductive layerin such a manner as to satisfy at least one of the following conditions:(A) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and

(B) a polymer in the second conductive layer is present with a higherdensity at the surface of the layer in contact with the first conductivelayer than at the surface not in contact with the first conductivelayer.

Thus, the present invention provides the following conductive porouslayer for batteries, and production method thereof.

Item 1. A conductive porous layer for batteries comprising a laminatecomprising a first conductive layer and a second conductive layer,

the first conductive layer comprising at least a conductive carbonmaterial and a polymer, and

the second conductive layer comprising at least a conductive carbonmaterial and a polymer, and

the conductive porous layer satisfying at least one of the followingconditions:

(A) the polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and

(B) the polymer in the second conductive layer is present with a higherdensity at the surface of the layer in contact with the first conductivelayer than at the surface not in contact with the first conductivelayer.

Item 2. The conductive porous layer for batteries according to Item 1,wherein the glass transition temperature of the polymer in the firstconductive layer is −100 to 300° C.

Item 3. The conductive porous layer for batteries according to Item 1 or2, wherein the glass transition temperature of the polymer in the secondconductive layer is −100 to 300° C.

Item 4. The conductive porous layer for batteries according to any oneof Items 1 to 3 that satisfies both of the above conditions (A) and (B).

Item 5. The conductive porous layer for batteries according to accordingto any one of items 1 to 4, wherein the conductive carbon material inthe second conductive layer is conductive carbon fibers with an averagefiber diameter of 5 μm or more and/or conductive carbon particles withan average particle diameter of 5 μm or more.Item 6. The conductive porous layer for batteries according to any oneof Items 1 to 5, which is a gas diffusion layer for fuel cells or aconductive porous layer for metal-air batteries.Item 7. A method for producing the conductive porous layer for batteriesaccording to any one of Items 1 to 6, the method comprising the stepsof:(I) applying a first conductive layer-forming paste composition to asubstrate and drying, wherein the composition comprises at least aconductive carbon material and a polymer, and then detaching theresulting first conductive layer from the substrate to produce a firstconductive layer having a polymer with a higher density at one sidesurface than at the opposite side surface,(II) applying a second conductive layer-forming paste composition to asubstrate and drying, wherein the composition comprises a conductivecarbon material and a polymer, and then detaching the resulting secondconductive layer from the substrate to produce a second conductive layerhaving a polymer with a higher density at one side surface than at theopposite side surface, and(III) disposing the first conductive layer and the second conductivelayer in such a manner as to satisfy at least one of the followingconditions:(A) the polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and(B) the polymer in the second conductive layer is present with a higherdensity at the surface of the layer in contact with the first conductivelayer than at the surface not in contact with the first conductivelayer; andperforming hot-pressing for bonding.Item 8. The method according to Item 7, wherein the polymer in step (I)has a glass transition temperature of −100 to 300° C.Item 9. The method according to Item 7 or 8, wherein the polymer in step(II) has a glass transition temperature of −100 to 300° C.Item 10. The method according to any one of Items 7 to 9, wherein step(III) is a step of disposing the first conductive layer and the secondconductive layer in such a manner as to satisfy both of the conditions(A) and (B), and performing hot-pressing for bonding.Item 11. The method according to any one of Items 7 to 10, wherein theconductive carbon material in step (II) is conductive carbon fibers withan average fiber diameter of 5 μm or more and/or conductive carbonparticles with an average particle diameter of 5 μm or more.Item 12. A membrane-electrode assembly for batteries comprising:

a catalyst layer laminated membrane comprising a catalyst layer, anelectrolyte membrane, and a catalyst layer that are sequentiallylaminated; and

the conductive porous layer for batteries according to any one of Items1 to 5 laminated on one or both sides of the catalyst layer laminatedmembrane in such a manner that the first conductive layer is in contactwith the catalyst layer.

Item 13. A battery comprising the membrane-electrode assembly forbatteries according to Item 12.

1. Conductive Porous Layer for Batteries

The conductive porous layer for batteries according to the presentinvention comprises a laminate comprising a first conductive layer and asecond conductive layer. The first conductive layer comprises at least aconductive carbon material and a polymer. The second conductive layercomprises at least a conductive carbon material and a polymer. Both ofthe polymers in the first conductive layer and the second conductivelayer preferably have a glass transition temperature (Tg) in the rangeof −100 to 300° C. There is no particular limitation on the type ofbattery for which the conductive porous layer of the present inventionis used insofar as the battery uses a gas as an active material of anegative or positive electrode. Examples of batteries include fuelcells, metal-air batteries, and the like.

First Conductive Layer

The first conductive layer comprises at least a conductive carbonmaterial and a polymer. The thickness of the first conductive layer isnot particularly limited. The preferable thickness of the firstconductive layer is typically about 1 to 150 μm, and particularlypreferably about 5 to 100 μm. In the present invention, a gas diffusionlayer with excellent gas diffusivity, gas permeability, water managementproperties, etc., can be provided by forming the first conductive layer.

Conductive Carbon Material

Examples of conductive carbon materials include, but are not limited to,conductive carbon particles, conductive carbon fibers, and the like.

Conductive Carbon Particles

Any carbon material that is conductive may be used as conductive carbonparticles, and known or commercially available materials can be used.Examples of such carbon materials include carbon blacks such as channelblack, furnace black, ketjen black, acetylene black, and lamp black;graphite; active charcoal; and the like. Such carbon materials can beused singly, or in a combination of two or more. The incorporation ofsuch conductive carbon particles can enhance the conductivity of theconductive porous layer.

When a carbon black is used as conductive carbon particles, the averageparticle diameter (arithmetic average particle diameter) of the carbonblack is not limited. The preferable average particle diameter thereofis typically about 5 to 200 nm, and particularly preferably about 5 to100 nm. When a carbon black aggregate is used, the preferable averageparticle diameter thereof is about 10 to 600 nm, and particularlypreferably about 50 to 500 nm. When graphite, active charcoal, or thelike is used, the preferable average particle diameter thereof is about500 nm to about 40 μm, and particularly preferably about 1 to 35 μm. Theaverage particle diameter of the conductive carbon particles can bemeasured, for example, by an LA-920 particle size distribution analyzer,produced by Horiba, Ltd.

Conductive Carbon Fibers

Incorporation of conductive carbon fibers can improve the quality of thesurface coated with the first conductive layer-forming pastecomposition, and can also provide a sheet-like first conductive layerwith high strength. Examples of conductive carbon fibers that can beused in the first conductive layer include, but are not limited to,vapor-grown carbon fibers (VGCF (registered trademark)), carbonnanotubes, carbon nanocaps, carbon nanowalls, and the like. Suchconductive carbon fibers may be used singly, or in a combination of twoor more.

The fiber diameter of the conductive carbon fibers is not particularlylimited. The preferable average fiber diameter thereof is about 50 to450 nm, and particularly preferably about 100 to 250 nm. The use of suchconductive carbon fibers can increase the nanometric fine pore volume,and is expected to provide effects such as flooding tolerance due toenhanced drainability and gas diffusion performance. The fiber length ofthe conductive carbon fibers is also not limited. The preferable averagefiber length thereof is about 4 to 500 μm, particularly about 4 to 300μm, more preferably about 4 to 50 μm, and particularly preferably about10 to 20 μm. The preferable average aspect ratio thereof is about 5 to600, and particularly preferably about 10 to 500. The fiber diameter,fiber length, and aspect ratio of the conductive carbon fibers can bemeasured from images measured under a scanning electron microscope(SEM), etc.

Polymer

The polymer is not particularly limited, and known or commerciallyavailable materials can be used. The polymer preferably has a glasstransition temperature of about −100 to 300° C., more preferably −60 to250° C., even more preferably about −30 to 220° C., and particularlypreferably about −20 to 210° C. Specific examples of polymers includeion-conductive polymer resins (e.g., Nafion), vinyl acetate resins,styrene-acrylic copolymer resins, styrene-vinyl acetate copolymerresins, ethylene-vinyl acetate copolymer resins, polyester-acryliccopolymer resins, urethane resins, acrylic resins, phenolic resins,polyvinylidene fluoride (PVDF), and the like. Other examples thereofinclude hexafluoropropylene-vinylidene fluoride copolymers,trifluorochloroethylene-vinylidene fluoride copolymers, and likefluororubbers, silicone rubbers, and the like. Such polymers may be usedsingly, or in a combination of two or more.

The use of an elastomer such as fluororubber as a polymer can increasethe flexibility of the first conductive layer, and also increase itsadhesion to other layers due to a low Tg of the elastomer. In thisspecification, the term “fluororubber” refers to a material having a Tgof about −30 to 100° C. Thus, with the use of such a material, amultilayer conductive porous sheet can be easily produced.

As the elastomer, an elastomer emulsion (a suspension in which elastomerparticles are dispersed) may be used, or an elastomer dissolved in asolvent may be used. In the case of using an elastomer emulsion, anemulsion prepared by dispersing an elastomer in a solvent, or acommercially available product can be used. Examples of the solventinclude water, ethanol, propanol, and the like. When an elastomerdissolved in a solvent is used, examples of the solvent includeN-methylpyrrolidone (NMP), methyl ethyl ketone (MEK), toluene, vinylacetate, dimethylacetamide (DMA), isopropyl alcohol (IPA), and the like.

To impart water repellency to the first conductive layer, awater-repellent resin, such as a fluorine-based resin, may be used. Inparticular, when a polymer with poor water repellency is used as thepolymer, the use of a water-repellent resin is effective for increasingwater repellency. Examples of such fluorine-based resins includepolytetrafluoroethylene resin (PTFE), fluorinated ethylene propyleneresin (FEP), perfluoroalkoxy resin (PFA), and the like.

In the present invention, the first conductive layer-forming pastecomposition may comprise a dispersant, alcohol, etc., in addition to theabove conductive carbon material and polymer, as long as the effect ofthe present invention is not impaired.

Dispersant

The dispersant may be any dispersant that can disperse a conductivecarbon material and a polymer in water. Known or commercially availabledispersants can be used. Examples of such dispersants include nonionicdispersants such as polyoxyethylene distyrenated phenyl ether,polyoxyethylene alkylene alkyl ether, and polyethylene glycol alkylether; cationic dispersants such as alkyltrimethylammonium salts,dialkyl dimethyl ammonium chlorides, and alkylpyridinium chlorides; andanionic dispersants such as polyoxyethylene fatty acid esters and acidicgroup-containing structure-modified polyacrylate. Such dispersants maybe used alone, or in a combination of two or more.

Alcohol

The alcohol is not particularly limited, and known or commerciallyavailable alcohols can be used. Examples of such alcohols includemonohydric or polyhydric alcohols having about 1 to 5 carbon atoms.Specific examples thereof include methanol, ethanol, 1-propanol,isopropanol, 1-butanol, 1-pentanol, and the like.

Second Conductive Layer

The second conductive layer comprises at least a conductive carbonmaterial and a polymer. The thickness of the second conductive layer isnot particularly limited. The preferable thickness thereof is typicallyabout 30 to 300 μm, and particularly preferably about 50 to 250 μm. Inthe present invention, a conductive porous layer with excellent filmstrength, gas permeability, and gas diffusivity can be provided byforming the second conductive layer.

Conductive Carbon Material

Examples of conductive carbon materials include, but are not limited to,conductive carbon particles, conductive carbon fibers, and the like.

Conductive Carbon Fibers

Incorporation of conductive carbon fibers enables the production of asheet-like second conductive layer with high strength. The conductivecarbon fiber used in the second conductive layer is not particularlylimited, and examples thereof include PAN (polyacrylonitrile)-basedcarbon fibers, pitch-based carbon fibers, and the like.

The fiber diameter of the conductive carbon fibers is not particularlylimited. The preferable average fiber diameter thereof is about 5 to 20μm, and particularly preferably about 6 to 15 μm. The use of suchconductive carbon fibers can produce a high-strength film; andfurthermore, the formation of fine pores having a micrometric diametercan provide high gas permeability. The fiber length of the conductivecarbon fibers is not particularly limited. The preferable average fiberlength thereof is 5 μm to 1 mm, and particularly preferably about 10 to600 μm. The preferable average aspect ratio thereof is about 1 to 50,and particularly preferably about 2 to 40. The fiber diameter, fiberlength, and aspect ratio of the conductive carbon fibers can be measuredfrom images measured under a scanning electron microscope (SEM), etc.

Conductive Carbon Particles

A second conductive layer with high gas permeability and gas diffusivitycan be produced by using conductive carbon particles. Examples ofconductive carbon particles that can be used in the second conductivelayer include graphite, active charcoal, and the like.

The particle diameter of conductive carbon particles is not particularlylimited. The preferable average particle diameter thereof is preferablyabout 5 to 100 μm, and particularly preferably about 6 to 80 μm. Theaverage particle diameter of the conductive carbon particles can bemeasured, for example, by an LA-920 particle size distribution analyzerproduced by Horiba, Ltd.

The above conductive carbon materials may be used singly, or as amixture of two or more. When two or more types of conductive carbonmaterials are used, both conductive carbon fibers and conductive carbonparticles can be used.

Polymer

The polymer may be the same material as that used in the firstconductive layer. Specifically, the polymer preferably has a Tg of about−100 to 300° C., more preferably about −60 to 250° C., even morepreferably about −30 to 220° C., and particularly preferably about −20to 210° C. Specific examples of such polymers include ion-conductivepolymer resins (e.g., Nafion), vinyl acetate resins, styrene-acryliccopolymer resins, styrene-vinyl acetate copolymer resins, ethylene-vinylacetate copolymer resins, polyester-acrylic copolymer resins, urethaneresins, acrylic resins, phenolic resins, polyvinylidene fluoride (PVDF),and the like. Other examples thereof include fluororubbers such ashexafluoropropylene-vinylidene fluoride copolymers andtrifluorochloroethylene-vinylidene fluoride copolymers, siliconerubbers, and the like. Such polymers may be used singly, or in acombination of two or more.

In the present invention, the second conductive layer-forming pastecomposition may comprise a fluorine-based resin, a dispersant, alcohol,etc., in addition to the above conductive carbon material and polymer,as long as the effect of the present invention is not impaired. Usablefluorine-based resins, dispersants, and alcohols may be the samematerials as used in the first conductive layer.

Characteristics of the First Conductive Layer and the Second ConductiveLayer

In the present invention, the front and back sides of each of the firstconductive layer and the second conductive layer have differentdensities of the polymer component. That is, the first conductive layeror the second conductive layer has a polymer with a higher density atone side surface than at the opposite side surface. In the presentinvention, when the first or second conductive layer comprises two ormore types of polymers, at least one type of polymer is preferablypresent with a higher density at one side surface of the layer than atthe opposite side surface. The distribution state of the polymercomponent in the first conductive layer and the second conductive layercan be confirmed, for example, by analyzing both surfaces usingenergy-dispersive X-ray fluorescence spectrometry, etc. The distributionof the polymer component can also be analyzed by energy-dispersive X-rayfluorescence analysis in the layer's cross-sectional direction. When theelement specific to the polymer cannot be detected by energy-dispersiveX-ray fluorescence analysis, for example, in the case of using astyrene-acrylic acid rubber, the functional group resulting from thepolymer can be observed by a Fourier transform infraredspectrophotometer, etc.

In the present invention, the pore diameter distribution of the firstconductive layer is preferably such that the volume of pores having adiameter of 10 nm to 5 μm, and preferably 20 nm to 5 μm, accounts for atleast 50% of the total pore volume. The pore diameter distribution canbe measured, for example, by an AutoPore IV 9500 automatic porosimeter(produced by Shimadzu Corporation). The above-mentioned pore diameterdistribution can be achieved by using, for example, conductive carbonfibers with an average fiber diameter of about 50 to 450 nm, a polymer,conductive carbon particles with an average particle diameter(arithmetic average particle diameter) of 5 to 200 nm, or conductivecarbon particles (e.g., graphite, active charcoal, etc.) with an averageparticle diameter of 500 nm to 40 μm.

The pore diameter distribution of the second conductive layer ispreferably such that the volume of pores having a diameter of 5 to 100μm, and preferably 5 to 50 μm, accounts for at least 50% of the totalpore volume. The above pore diameter distribution can be achieved, forexample, by using conductive carbon fibers with an average fiberdiameter of about 5 μm or more, using a polymer, etc.

Method for Producing the First Conductive Layer and the SecondConductive Layer

In the present invention, the first conductive layer can be obtained,for example, by applying the first conductive layer-forming pastecomposition to a substrate, and drying the composition; and thendetaching the substrate. The second conductive layer can also beobtained by applying the second conductive layer-forming pastecomposition to a substrate, and drying the composition; and thendetaching the substrate.

When the first conductive layer and the second conductive layer areformed by the above method, the proportion of the polymer component thatis present at the surfaces of the first conductive layer and the secondconductive layer can be adjusted by utilizing the phenomenon, occurringduring the drying of the paste composition, in which the polymercomponent contained in the first conductive layer-forming pastecomposition or in the second conductive layer-forming paste compositionsegregates from the side not in contact with the substrate toward theside in contact with the substrate. Accordingly, the density of thepolymer component at one side surface of the layer can be increased byadjusting the amount of polymer used, viscosity of the pastecomposition, particle diameter in the case of using an elastomeremulsion as a polymer, drying time, specific gravity of the carbonmaterial (e.g., conductive carbon particles, conductive carbon fibers,etc.), functional group present at the surface of the carbon material(e.g., conductive carbon particles, conductive carbon fibers, etc.), andthe like. In particular, as the viscosity of the paste compositionlowers and the drying time lengthens, the resin tends to segregate (seeTable 1).

Content

The first conductive layer-forming paste composition may comprise, forexample, about 30 to 200 parts by weight (particularly 40 to 150 partsby weight) of a polymer, about 0 to 100 parts by weight (particularly 5to 50 parts by weight) of a dispersant, and about 0 to 1,100 parts byweight (particularly 100 to 1,000 parts by weight) of a solvent, such asalcohol, based on 100 parts by weight of conductive carbon particles(the total amount of conductive carbon particles and conductive carbonfibers, when conductive carbon fibers are contained). When conductivecarbon particles and conductive carbon fibers are both contained, theratio of conductive carbon particles to conductive carbon fibers ispreferably in the range of about 9:1 (weight ratio) to about 1:9 (weightratio), and is particularly preferably about 8:2 (weight ratio) to about2:8 (weight ratio). To enhance water repellency, the composition maycontain a fluorine-based resin in an amount of about 5 to 250 parts byweight (particularly 10 to 200 parts by weight). When an elastomeremulsion is used as a polymer, the solids content is preferably withinthe above-mentioned range. When the first conductive layer-forming pastecomposition contains a resin component having a Tg outside the range of−100 to 300° C., the ratio of the polymer having a Tg within the rangeof −100 to 300° C. to the resin component having a Tg outside the rangeof −100 to 300° C. is preferably in the range of about 9.5:0.5 (weightratio) to about 4:6 (weight ratio), and is particularly preferably about9:1 (weight ratio) to about 5:5 (weight ratio).

The second conductive layer-forming paste composition may comprise, forexample, about 5 to 150 parts by weight (particularly 10 to 100 parts byweight) of a polymer, 0 to 100 parts by weight (particularly 5 to 50parts by weight) of a dispersant, and 0 to 500 parts by weight(particularly about 10 to 400 parts by weight) of a solvent, such asalcohol, based on 100 parts by weight of the conductive carbon material.When conductive carbon particles and conductive carbon fibers are bothcontained, the ratio of conductive carbon particles to conductive carbonfibers is preferably in the range of about 9:1 (weight ratio) to about1:9 (weight ratio), and is particularly preferably about 8:2 (weightratio) to about 2:8 (weight ratio). When an elastomer emulsion is usedas a polymer, the solids content is preferably within theabove-mentioned range. When the second conductive layer-forming pastecomposition comprises a resin component having a Tg outside the range of−100 to 300° C., the ratio of the polymer having a Tg within the rangeof −100 to 300° C. to the resin component having a Tg outside the rangeof −100 to 300° C. is preferably in the range of about 9:1 (weightratio) to 4:6 (weight ratio), and is particularly preferably about 8:2(weight ratio) to 5:5 (weight ratio).

The first conductive layer-forming paste composition and the secondconductive layer-forming paste composition comprise the aforementionedcomponents.

The substrate is not particularly limited insofar as the pastecomposition can be applied thereto. Known or commercially availablesubstrates can be used widely. Examples of such substrates includepolyimide, polyethylene terephthalate, polyparabanic acid, aramid,polyamide (nylon), polysulfone, polyether sulphone, polyphenylenesulfide, polyether ether ketone, polyether imide, polyarylate,polyethylene naphthalate, polypropylene, and like polymeric films.Further, ethylene-tetrafluoroethylene copolymer (ETFE),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),polytetrafluoroethylene (PTFE), or the like can also be used. Amongthese, polymeric films that are highly heat-resistant and easilyavailable are preferable. For example, polyethylene terephthalate,polyethylene naphthalate, polytetrafluoroethylene (PTFE), polyimide, andlike films are preferable.

The substrate preferably has a release layer formed thereon. Forexample, the release layer may comprise a known wax. As a substratehaving a release layer formed thereon, a film coated with SiOx, afluororesin, or the like may be used.

It is preferable from the viewpoint of ease of handling and costefficiency that the thickness of the substrate is typically about 6 to100 μm, and particularly preferably about 10 to 60 μm.

The coating method is preferably application using known or commerciallyavailable doctor blades and like blades; wire bars; squeegees, and likeinstruments; applicators; die coaters; etc.

The amount of each paste composition to be applied is not particularlylimited. The composition for forming a first conductive layer ispreferably applied in such an amount that the resulting first conductivelayer has a thickness of about 1 to 150 μm, and more preferably about 5to 100 μm. The composition for forming a second conductive layer ispreferably applied in such an amount that the resulting secondconductive layer has a thickness of about 30 to 300 μm, and preferablyabout 50 to 250 μm.

The drying conditions are also not limited. The dry conditions can besuitably changed according to the conditions, such as the volatilizationtemperature of the solvent used (e.g., alcohol) (for example, about 150°C.), and the glass transition temperature of the polymer.

After the first conductive layer and the second conductive layer areobtained by drying, the layers may be further subjected to drying at ahigher temperature (e.g., about 150 to 500° C.), if necessary.

Further, the first conductive layer and the second conductive layer maybe treated on the surface (in particular, on the surface in contact withthe other layer). Examples of the surface treatment include mechanicaltreatment to physically roughen the surface by a metallic brush,sandblasting, or the like, matting treatment, corona dischargetreatment, plasma discharge treatment, ultraviolet treatment, etc.

Characteristics of the Conductive Porous Layer for Batteries

In the present invention, the conductive porous layer for batteriescomprises a laminate comprising the aforementioned first conductivelayer and second conductive layer. The first conductive layer and thesecond conductive layer are laminated in such a manner as to satisfy atleast one of (preferably both of) the following conditions:

(A) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer; and

(B) a polymer in the second conductive layer is present with a higherdensity at the surface of the layer in contact with the first conductivelayer than at the surface not in contact with the first conductivelayer.

Specifically, the first conductive layer and the second conductive layerare laminated in such a manner as to satisfy at least one of thefollowing conditions (preferably satisfy condition (b)):

(a) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer not in contact with the secondconductive layer than at the surface of the layer in contact with thesecond conductive layer, and a polymer in the second conductive layer ispresent with a higher density at the surface of the layer in contactwith the first conductive layer than at the surface not in contact withthe first conductive layer;

(b) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and a polymer in the second conductive layer ispresent with a higher density at the surface of the layer in contactwith the first conductive layer than at the surface not in contact withthe first conductive layer; and

(c) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and a polymer in the second conductive layer ispresent with a higher density at the surface of the layer not in contactwith the first conductive layer than at the surface in contact with thefirst conductive layer.

Thus, in the present invention, one or both of the surfaces at which apolymer (at least one type of polymer, when the first conductive layercontains a plurality of polymers) in the first conductive layer ispresent with a higher density, and the surface at which a polymer in thesecond conductive layer (at least one type of polymer when the secondconductive layer contains a plurality of polymers) is present with ahigher density are located at the interface between the first conductivelayer and the second conductive layer. This can enhance the adhesionbetween the first conductive layer and the second conductive layer.Further, in the present invention, the first conductive layer is formedby applying the first conductive layer-forming paste composition to asubstrate and drying, and then detaching the resulting layer from thesubstrate, after which the first conductive layer and the secondconductive layer are laminated. This can reduce film thicknessvariation, compared to the method of applying the composition toconventionally used carbon paper or the like and drying.

Conductive Porous Substrate

The conductive porous layer of the present invention may comprise aknown or commercially available gas diffusion layer (e.g., carbon paper,carbon cloth, carbon felt, etc.) as a conductive porous substrate formedon the second conductive layer.

For exemplary purposes with respect to the properties of typical carbonpaper, the properties of TGP-H-060 produced by Toray Industries areshown below:

thickness: 190 μm;

electrical resistance: 80 mΩ-cm in the thickness direction, 5.8 mΩ-cm inthe surface direction;

porosity: 78%;

bulk density: 0.44 g/cm³;

surface roughness: 8 μm.

The thickness of the carbon paper, etc., is not limited. Preferably, thethickness is typically about 50 to 1,000 μm, and more preferably about100 to 400 μm.

A conductive porous substrate previously subjected to a water-repellenttreatment is preferably used. This can further enhance the waterrepellency of the conductive porous material.

The water-repellent treatment may be, for example, a method comprisingimmersing the conductive porous substrate in an aqueous dispersion of afluorine-based resin, etc. The fluorine-based resin may be theaforementioned resin, or the like. In this method, a dispersant asmentioned above may be used to disperse a fluorine-based resin in water,and an aqueous suspension containing a fluorine-based resin and anaqueous dispersant is preferably used as the aqueous dispersion.

The amount of the fluorine-based resin in the aqueous dispersion is notparticularly limited and may be, for example, about 1 to 30 parts byweight, and particularly preferably about 2 to 20 parts by weight, per100 parts by weight of water.

Method for Producing a Conductive Porous Layer

The conductive porous layer of the present invention can be produced bylaminating a first conductive layer, a second conductive layer, andoptionally one or more other layers, and performing hot-pressing. Theproduced conductive porous layer for batteries of the present inventionmay be laminated on one side or both sides of the catalyst layerlaminated membrane or of the electrolyte membrane described below, andbonded to produce a membrane-electrode assembly. Alternatively, thefirst conductive layer and the second conductive layer may be laminatedin this order on one or both sides of the catalyst layer laminatedmembrane or of the electrolyte described below to produce the conductiveporous layer for batteries and membrane-electrode assembly of thepresent invention at the same time.

More specifically, first, the first conductive layer is formed by thefollowing step.

(I) After a first conductive layer-forming paste composition comprisingat least conductive carbon particles and a polymer (preferably a polymerhaving a glass transition temperature of −30 to 220° C.) is applied to asubstrate and dried, the resulting first conductive layer is detachedfrom the substrate to produce a first conductive layer having a polymerwith a higher density at one side surface than at the opposite sidesurface.

Subsequently, the second conductive layer is formed by the followingstep.

(II) After a second conductive layer-forming paste compositioncomprising at least conductive carbon particles and a polymer(preferably a polymer having a glass transition temperature of −30 to220° C.) is applied to a substrate and dried, the resulting secondconductive layer is detached from the substrate to produce a secondconductive layer having a polymer with a higher density at one sidesurface than at the opposite side surface.

The conditions for producing the first conductive layer and the secondconductive layer are as described above.

Further, the following step is performed to produce the conductiveporous layer for batteries of the present invention.

(III) The first conductive layer and the second conductive layer aredisposed in such a manner as to satisfy at least one of the followingconditions:

(A) a polymer in the first conductive layer is present with a higherdensity at the surface of the layer in contact with the secondconductive layer than at the surface not in contact with the secondconductive layer, and

(B) a polymer in the second conductive layer is present with a higherdensity at the surface of the layer in contact with the first conductivelayer than at the surface not in contact with the first conductivelayer; and performing hot-pressing for bonding.

In the above step (III), the hot-pressing temperature is notparticularly limited. It is preferable that the hot-pressing temperatureis not lower than the Tg of the polymers contained in the firstconductive layer and in the second conductive layer. When the Tg of thepolymer contained in the first conductive layer and the Tg of thepolymer contained in the second conductive layer are different, thehot-pressing temperature is preferably not lower than the lower Tg. Whenthe first conductive layer or the second conductive layer comprises apolymer having a Tg outside the range of −100 to 300° C., thehot-pressing temperature is preferably not lower than the lowest Tgamong the Tg values of the polymers contained in the first conductivelayer and the second conductive layer.

After the conductive porous layer comprising a laminate comprising thefirst conductive layer and the second conductive layer is produced inthis manner, the layer may be further dried at a higher temperature(e.g., about 150 to 500° C.), if necessary.

2. Membrane-Electrode Assembly for Batteries

The conductive porous layer for batteries of the present invention canalso be used to produce a membrane-electrode assembly for batteries.More specifically, the conductive porous layer of the present inventionis preferably stacked on one side or both sides of the catalyst layerlaminated membrane comprising a catalyst layer, an electrolyte membrane,and a catalyst layer that are sequentially laminated. In this case, theconductive porous layer of the present invention functions as a gasdiffusion layer. Taking a membrane-electrode assembly for solid polymerfuel cells as an example, the constituent materials and the method forproducing the catalyst layer laminated membrane are explained below.

Electrolyte Membrane

The electrolyte membrane may be any ion-conductive electrolyte membrane.Known or commercially available electrolyte membranes, such as hydrogenion-conductive electrolyte membranes and hydroxide ion-conductiveelectrolyte membranes, can be used. Examples of hydrogen ion-conductiveelectrolyte membranes include “Nafion” (registered trademark) membraneproduced by Du Pont, Inc., “Flemion” (registered trademark) membrane byAsahi Glass Co., Ltd., “Aciplex” (registered trademark) membrane byAsahi Kasei Corporation, “GoreSelect” (registered trademark) membrane byGore & Assoc. Inc., and the like. Examples of hydroxide ion-conductiveelectrolyte membranes includes hydrocarbon-based electrolyte membranessuch as Aciplex (registered trademark) A-201, A-211, A-221, etc.,produced by Asahi Kasei Corporation, Neosepta (registered trademark)AM-1 and AHA by Tokuyama Corporation, and the like; and fluororesinelectrolyte membranes such as Tosflex (registered trademark) IE-SF34 byTosoh Corporation, Fumapem (registered trademark) FAA by FuMA-Tech GmbH,and the like.

It is preferable that the thickness of the electrolyte membrane istypically about 20 to 250 μm, and particularly preferably about 20 to150 μm.

Catalyst Layer

As the catalyst layer, a known or commercially availableplatinum-containing catalyst layer (a cathode catalyst or an anodecatalyst) can be used. Specifically, the catalyst layer is preferablyformed of a dried product of the paste composition for forming acatalyst layer comprising (1) carbon particles supporting catalystparticles and (2) an ion-conductive polymer electrolyte (preferably ahydrogen ion-conductive polymer electrolyte).

Any catalyst particles that can cause an oxidation-reduction reaction(oxidation of hydrogen at the anode, and reduction of oxygen at thecathode) and that have catalytic activity can be used as the catalystparticles. Examples of catalyst particles include platinum, platinumalloys, platinum compounds, and the like. Examples of platinum alloysinclude alloys of platinum and at least one metal selected from thegroup consisting of ruthenium, palladium, nickel, molybdenum, iridium,iron, and cobalt.

Examples of ion-conductive polymer electrolytes includeperfluorosulfonic acid-based fluorine ion-exchange resins. Specificexamples thereof include perfluorocarbon sulfonic acid-based polymers(PFS polymers) in which a C—H bond of a hydrocarbon-based ion-exchangemembrane is replaced with a fluorine.

The thickness of the catalyst layer is not particularly limited. Thepreferable thickness thereof is typically about 1 to 100 μm, and morepreferably about 2 to 50 μm.

In the catalyst layer, fluororesins and non-polymer fluorine materials,such as fluorinated pitch, fluorinated carbon, and graphite fluoride,can be added as a water repellent.

Method for Producing the Catalyst Layer Laminated Membrane

The catalyst layer laminated membrane can be produced, for example, bydisposing a catalyst layer transfer film in such a manner that thecatalyst layer and the electrolyte membrane are face-to-face, pressingthe layers under heating to transfer the catalyst layer to theelectrolyte membrane, and then detaching the transfer film. A catalystlayer laminated membrane comprising a catalyst layer on both sides ofthe electrolyte membrane can be produced by repeating this operationtwice. In consideration of work efficiency, etc., simultaneouslylaminating the catalyst layer on both sides of the electrolyte membraneis preferable.

For the transfer, it is preferable to press the layers from thesubstrate film side of the catalyst layer transfer film using a knownpressing machine, etc. To avoid poor transfer, the pressure level istypically about 0.5 to 10 MPa, and particularly preferably about 1 to 8MPa. To avoid poor transfer, the face to be pressed is preferably heatedduring the pressing operation. Preferably, the heating temperature isappropriately changed according to the type of electrolyte membrane tobe used.

The substrate film is not particularly limited, and the same substratesas mentioned above can be used. Examples of substrate films includepolymeric films such as polyimide, polyethylene terephthalate (PET),polysulfone, polyether sulphone, polyphenylene sulfide, polyether etherketone, polyether imide, polyarylate, polyethylene naphthalate (PEN),polyethylene, polypropylene, and polyolefin. Heat-resistant fluororesinssuch as ethylene-tetrafluoroethylene copolymer (ETFE),tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), andpolytetrafluoroethylene (PTFE) can also be used. Among these,inexpensive and easily available polymeric films are preferable, andpolyethylene terephthalate, etc., are more preferable.

In view of workability, cost efficiency, etc., of forming the catalystlayer on the substrate film, it is preferable that the thickness of thesubstrate film is typically about 6 to 150 μm, and particularly about 12to 75 μm.

The substrate film may have a release layer formed thereon. Examples ofrelease layers include a layer comprising a known wax, a plastic filmcoated with a known SiOx or a fluorine-based resin, and the like. Asubstrate film comprising a film with high release properties formedthereon, such as a laminate of a PET substrate and a heat-resistantfluororesin substrate; and like structured substrate films, are alsousable.

3. Battery

The battery of the present invention (e.g., solid polymer fuel cells,metal-air batteries, etc.) can be produced by providing a known orcommercially available separator, terminals, etc., in the abovemembrane-electrode assembly or conductive porous layer.

When the conductive porous layer of the present invention is used formetal-air batteries, the use is not particularly limited, and can beused, for example, in the following manner. The conductive porous layerof the present invention is stacked on one side of a positive electrodecatalyst layer to form a positive electrode; and a negative electrode isdisposed on the opposite side of the positive electrode catalyst layervia a separator. The space between the separator and the negativeelectrode catalyst layer (or between the negative electrode catalystlayer and the positive electrode catalyst layer) is filled with anelectrode. In this case, the conductive porous layer of the presentinvention functions as a gas diffusion layer. Because the conductiveporous layer of the present invention comprises a carbon material, itcan be used without providing the aforementioned positive electrodecatalyst layer. In this case, the conductive porous layer-forming layerfunctions as a catalyst layer and/or a gas diffusion layer.

The types of metal-air battery include lithium-air batteries, sodium-airbatteries, potassium-air batteries, magnesium-air batteries, calcium-airbatteries, zinc-air batteries, aluminum-air batteries, and iron-airbatteries. The metal-air battery may be a primary battery or a secondarybattery. The materials used to form the positive electrode catalystlayer, negative electrode, electrolyte, separator, and substrate may beknown or commercially available materials that are conventionally usedin metal-air batteries. The electrolyte may be in the form of a liquid,a gel, or a solid.

Advantageous Effects of Invention

According to the present invention, a conductive porous layer forbatteries that has a good adhesion between the first conductive layerand the second conductive layer and that has reduced film thicknessvariation in each conductive layer can be provided.

DESCRIPTION OF EMBODIMENTS

The present invention is explained in detail with reference to Examplesand Comparative Examples. The present invention is not limited to thefollowing embodiments.

Materials

The materials shown below were used for preparation of the firstconductive layer-forming paste composition and the second conductivelayer-forming paste composition.

Conductive carbon particles (1): Furnace black (Balkan xc72R: producedby Cabot Corporation), average molecular weight: 1000 to 3000, averageparticle diameter: 30 nm

Conductive carbon particles (2): CGB-35 (produced by Nippon GraphiteIndustries, Ltd.; average particle diameter: 35 μm)

Conductive carbon particles (3): Asahi HS-500 (produced by Asahi CarbonCo., Ltd.; average particle diameter: 38 nm)

Polymer (1): Nafion (a 5 wt % Nafion solution “DE-520” produced by DuPont, Inc., was used), Tg: 130° C.

Polymer (2): AP-2675 (produced by Showa Denko K.K.; emulsion using astyrene acrylic acid-based copolymer resin; solids content 50 wt %), Tg:0° C.

Polymer (3): TLX-1068-1 (produced by Showa Denko K.K.; emulsion using astyrene acrylic acid-based copolymer resin; solids content: 20 wt %),average particle diameter of 15 to 35 nm, Tg: 0° C.

Polymer (4): G-801 (produced by Daikin Industries, Ltd.;fluorine-containing rubber), Tg: 0° C.

Polymer (5): Solef 21216/1001 (produced by Solvay Solexis Inc.; PVDF),Tg: −30° C.

Polymer (6): Vinyrol PSA AV6020 (produced by Showa Denko K.K.; acrylicadhesive), Tg: −60° C.

Polymer (7): Solef 5130 (produced by Solvay Solexis Inc.; PVDF), Tg:−40° C.

Polymer (8): Shonol BRL-120Z (produced by Showa Denko K.K.; phenolresin; solids content: 70 wt %), Tg: 250° C.

Polymer (9): Polytetrafluoroethylene (PTFE) (AD911L produced by AsahiGlass Co., Ltd.; Tg: about 130° C.

Polymer (10): Polytetrafluoroethylene (PTFE) (Rubron L5 produced byDaikin Industries Ltd.; Tg: about 130° C.)

Conductive carbon fibers (1): VGCF (VGCF (registered trademark)(standard product): produced by Showa Denko K.K.; average fiberdiameter: 150 nm, average fiber length: 10 to 20 μm, and average aspectratio: 10 to 500)

Conductive carbon fibers (2): DONACARBO-Milled S-2404 (produced by OsakaGas Chemical; average fiber diameter: 13 μm, average fiber length: 40μm, and average aspect ratio: 3)

Conductive carbon fibers (3): Raheama R-A201 (produced by Teij in Ltd.;average fiber diameter: 8 μm, average fiber length: 50 μm, and averageaspect ratio: 6)

Conductive carbon fibers (4): S241 (produced by Osaka Gas Chemical Co.,Ltd.; average fiber diameter: 13 μm, average fiber length: 130 μm, andaverage aspect ratio: 10)

Dispersant: Emulgen A-60 (produced by Kao Corporation)

Examples 1 to 15 and Comparative Examples 1 to 7

In the following examples and comparative examples, both the firstconductive layer and the second conductive layer have a size of 50×50mm².

Example 1

(i) First Conductive Layer

Conductive carbon particles (1) (100 parts by weight), Polymer (9) (50parts by weight), conductive carbon fibers (1) (75 parts by weight),polymer (1) (1250 parts by weight (solids content: 62.5 parts byweight)), the dispersant (25 parts by weight), and water (350 parts byweight) were subjected to media dispersion to prepare a first conductivelayer-forming paste composition. The first conductive layer-formingpaste composition was applied on a polyethylene terephthalate (PET)film, on which a release layer had been formed, to a thickness of about50 μm using an applicator. Regarding the viscosity of the pastecomposition, the shear viscosity was about 150 mPa·s at a shear rate of1000 (1/s). The viscosity of the paste composition was measured using aPhysica MCR301 produced by Anton Paar GmbH (a cone-shaped jig with adiameter of 50 mm and an angle of 1° was used as a jig). The pastecompositions used in other Examples and Comparative Examples weremeasured in the same manner. Subsequently, drying was performed in adrying furnace set at 95° C. for about 15 minutes to produce a firstconductive layer.

(ii) Second Conductive Layer

Conductive carbon fibers (2) (100 parts by weight), polymer (2) (50parts by weight (solids content: 25 parts by weight)), the dispersant(25 parts by weight), polymer (1) (60 parts by weight (solids content: 3parts by weight)), and water (100 parts by weight) were subjected tomedia dispersion to prepare a second conductive layer-forming pastecomposition. The second conductive layer-forming paste composition wasapplied on a PET film, on which a release layer had been formed, to athickness of about 150 μm using an applicator. Regarding the viscosityof the paste composition, the shear viscosity was about 70 mPa·s at ashear rate of 1000 (1/s). Subsequently, drying was performed in a dryingfurnace set at 95° C. for about 40 minutes to produce a secondconductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(1) and (9)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymers (polymers (1) and(2)) with a higher density. Hot-pressing was then performed at apressing temperature of 100° C. and a pressing pressure of 7.5 kN, for apressing time of 2 minutes to produce the conductive porous layer ofExample 1.

Example 2

Using the same material compositions of Example 1, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (9)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a higher density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Example 2.

Example 3

Using the same material compositions of Example 1, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (9)) with a higher densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a lower density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Example 3.

Example 4

(i) First Conductive Layer

Conductive carbon particles (1) (100 parts by weight), conductive carbonfibers (1) (100 parts by weight), polymer (3) (1600 parts by weight(solids content: 320 parts by weight)), polymer (1) (1600 parts byweight (solids content: 80 parts by weight)), and ethanol (250 parts byweight) were subjected to media dispersion to prepare a first conductivelayer-forming paste composition. The first conductive layer-formingpaste composition was applied on a PET film, on which a release layerhad been formed, to a thickness of about 50 μm using an applicator.Regarding the viscosity of the paste composition, the shear viscositywas about 170 mPa·s at a shear rate of 1000 (1/s). Subsequently, dryingwas performed in a drying furnace set at 95° C. for about 15 minutes toproduce a first conductive layer.

(ii) Second Conductive Layer

Conductive carbon fibers (2) (100 parts by weight), polymer (2) (50parts by weight (solids content: 25 parts by weight)), the dispersant(25 parts by weight), polymer (1) (60 parts by weight (solids content: 3parts by weight)), and water (100 parts by weight) were subjected tomedia dispersion to prepare a second conductive layer-forming pastecomposition. The second conductive layer-forming paste composition wasapplied on a PET film, on which a release layer had been formed, to athickness of about 150 μm using an applicator. Regarding the viscosityof the paste composition, the shear viscosity was about 70 mPa·s at ashear rate of 1000 (1/s). Subsequently, drying was performed in a dryingfurnace set at 95° C. for about 40 minutes to produce a secondconductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(1) and (3)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymers (polymers (1) and(2)) with a higher density. Hot-pressing was then performed at apressing temperature of 100° C. and a pressing pressure of 7.5 kN, for apressing time of 2 minutes to produce the conductive porous layer ofExample 4.

Example 5

Using the same material compositions of Example 4, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (3)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a higher density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Example 5.

Example 6

Using the same material compositions of Example 4, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (3)) with a higher densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a lower density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Example 6.

Example 7

(i) First Conductive Layer

Polymer (4) was added to methyl ethyl ketone (MEK), and the mixture wasmaintained using a stirrer (media rotation speed: 300 rpm) at 80° C. for60 minutes, thereby obtaining a fluorine-containing rubber solutionhaving a solids content (polymer (4)) of 20 wt % in which polymer (4)was dissolved in the MEK. Subsequently, conductive carbon fibers (1)(100 parts by weight), conductive carbon particles (2) (85 parts byweight), the prepared fluorine-containing rubber solution having asolids content of 20 wt % (920 parts by weight (solids content: 184parts by weight), and MEK (1670 parts by weight) were subjected to mediadispersion to prepare a first conductive layer-forming pastecomposition. The first conductive layer-forming paste composition wasapplied on a PET film (Serapiru manufactured by Toray Industries Inc.),on which a release layer had been formed, to a thickness of about 50 μmusing an applicator. Regarding the viscosity of the paste composition,the shear viscosity was about 150 mPa·s at a shear rate of 1000 (1/s).Subsequently, drying was performed in a drying furnace set at 95° C. forabout 15 minutes to produce a first conductive layer.

(ii) Second Conductive Layer

Polymer (5) was added to MEK and the mixture was maintained using astirrer (media rotation speed: 300 rpm) at 80° C. for 60 minutes,thereby obtaining a PVDF solution having a solids content (polymer (5))of 10 wt % in which polymer (5) was dissolved in the MEK. Subsequently,conductive carbon fibers (3) (100 parts by weight), the prepared PVDFsolution (100 parts by weight (solids content: 10 parts by weight)), andMEK (50 parts by weight) were subjected to media dispersion to prepare asecond conductive layer-forming paste composition. The second conductivelayer-forming paste composition was applied on a PET film (Serapirumanufactured by Toray Industries Inc.), on which a release layer hadbeen formed, to a thickness of about 150 μm using an applicator.Regarding the viscosity of the paste composition, the shear viscositywas about 350 mPa·s at a shear rate of 1000 (1/s). Subsequently, dryingwas performed in a drying furnace set at 95° C. for about 40 minutes toproduce a second conductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymer (polymer(4)) with a higher density was disposed adjacent to the surface of thesecond conductive layer having the polymer (polymer (5)) with a higherdensity. Hot-pressing was then performed at a pressing temperature of100° C. and a pressing pressure of 7.5 kN, for a pressing time of 2minutes to produce the conductive porous layer of Example 7.

Example 8

Using the same material compositions of Example 7, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film (Serapirumanufactured by Toray Industries, Inc.), on which a release layer hadbeen formed, to a thickness of about 50 μm (the first conductive layer)and a thickness of about 150 μm (the second conductive layer) using anapplicator. The first conductive layer and the second conductive layerwere each individually detached from the PET film including the releaselayer, and the surface of the first conductive layer having the polymer(polymer (4)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymer (polymer (5)) with alower density. Hot-pressing was then performed at a pressing temperatureof 100° C. and a pressing pressure of 7.5 kN, for a pressing time of 2minutes to produce the conductive porous layer of Example 8.

Example 9

Using the same material compositions of Example 7, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymer (polymer (4)) with a lower density was disposedadjacent to the surface of the second conductive layer having thepolymer (polymer (5)) with a higher density. Hot-pressing was thenperformed at a pressing temperature of 100° C. and a pressing pressureof 7.5 kN, for a pressing time of 2 minutes to produce the conductiveporous layer of Example 9.

Example 10

(i) First Conductive Layer

Conductive carbon particles (1) (100 parts by weight), polymer (9) (50parts by weight), conductive carbon fibers (1) (75 parts by weight),polymer (1) (1250 parts by weight), the dispersant (25 parts by weight),and water (1050 parts by weight) were subjected to media dispersion toprepare a first conductive layer-forming paste composition. The firstconductive layer-forming paste composition was applied on a PET film, onwhich a release layer had been formed, to a thickness of about 50 μmusing an applicator. Regarding the viscosity of the paste composition,the shear viscosity was about 60 mPa·s at a shear rate of 1000 (1/s).Subsequently, drying was performed in a drying furnace set at 95° C. forabout 30 minutes to produce a first conductive layer.

(ii) Second Conductive Layer

Conductive carbon fibers (2) (100 parts by weight), polymer (2) (50parts by weight (solids content: 25 parts by weight)), the dispersant(25 parts by weight), polymer (1) (60 parts by weight (solids content: 3parts by weight)), and water (100 parts by weight) were subjected tomedia dispersion to prepare a second conductive layer-forming pastecomposition. The second conductive layer-forming paste composition wasapplied on a PET film, on which a release layer had been formed, to athickness of about 150 μm using an applicator. Regarding the viscosityof the paste composition, the shear viscosity was about 70 mPa·s at ashear rate of 1000 (1/s). Subsequently, drying was performed in a dryingfurnace set at 95° C. for about 30 minutes to produce a secondconductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(1) and (9)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymers (polymers (1) and(2)) with a higher density. Hot-pressing was then performed at apressing temperature of 100° C. and a pressing pressure of 7.5 kN, for apressing time of 2 minutes to produce the conductive porous layer ofExample 10.

Example 11

(i) First Conductive Layer

Polymer (5) was added to methyl ethyl ketone (MEK), and the mixture wasmaintained using a stirrer (media rotation speed: 300 rpm) at 80° C. for60 minutes, thereby obtaining a PVDF solution having a solids content(polymer (5)) of 10 wt % in which polymer (5) was dissolved in the MEK.Subsequently, conductive carbon particles (3) (100 parts by weight), theprepared PVDF solution having a solids content of 10 wt % (1000 parts byweight (solids content: 100 parts by weight)), and MEK (1125 parts byweight) were subjected to media dispersion to prepare a first conductivelayer-forming paste composition. The first conductive layer-formingpaste composition was applied on a PET film (Serapiru manufactured byToray Industries Inc.), on which a release layer had been formed, to athickness of about 50 μm using an applicator. Regarding the viscosity ofthe paste composition, the shear viscosity was about 150 mPa·s at ashear rate of 1000 (1/s). Subsequently, drying was performed in a dryingfurnace set at 95° C. for about 15 minutes to produce a first conductivelayer.

(ii) Second Conductive Layer

Polymer (5) was added to MEK, and the mixture was maintained using astirrer (media rotation speed: 300 rpm) at 80° C. for 60 minutes,thereby obtaining a PVDF solution having a solids content (polymer (5))of 10 wt % in which polymer (5) was dissolved in the MEK. Subsequently,conductive carbon particles (2) (100 parts by weight), the prepared PVDFsolution (100 parts by weight (solids content: 10 parts by weight)), andMEK (50 parts by weight) were subjected to media dispersion to prepare asecond conductive layer-forming paste composition. The second conductivelayer-forming paste composition was applied on a PET film (Serapirumanufactured by Toray Industries Inc.), on which a release layer hadbeen formed, to a thickness of about 150 μm using an applicator.Regarding the viscosity of the paste composition, the shear viscositywas about 200 mPa·s at a shear rate of 1000 (1/s). Subsequently, dryingwas performed in a drying furnace set at 95° C. for about 40 minutes toproduce a second conductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymer (polymer(5)) with a higher density was disposed adjacent to the surface of thesecond conductive layer having the polymer (polymer (5)) with a higherdensity. Hot-pressing was then performed at a pressing temperature of135° C. and a pressing pressure of 7.5 kN, for a pressing time of 2minutes to produce the conductive porous layer of Example 11.

Example 12

(i) First Conductive Layer

Conductive carbon particles (1) (100 parts by weight), polymer (10) (50parts by weight), polymer (6) (167 parts by weight), conductive carbonfibers (1) (76.7 parts by weight), and isopropanol (150 parts by weight)were subjected to media dispersion to prepare a first conductivelayer-forming paste composition. The first conductive layer-formingpaste composition was applied on a polyethylene terephthalate (PET)film, on which a release layer had been formed, to a thickness of about50 μm using an applicator. Regarding the viscosity of the pastecomposition, the shear viscosity was about 92 mPa·s at a shear rate of1000 (1/s). Subsequently, drying was performed in a drying furnace setat 95° C. for about 15 minutes to produce a first conductive layer.

(ii) Second Conductive Layer

Conductive carbon fibers (4) (100 parts by weight), polymer (5) (100parts by weight (solids content: 10 parts by weight)), and methyl ethylketone (50 parts by weight) were subjected to media dispersion toprepare a second conductive layer-forming paste composition. The secondconductive layer-forming paste composition was applied on a PET film, onwhich a release layer had been formed, to a thickness of about 150 μmusing an applicator. Regarding the viscosity of the paste composition,the shear viscosity was about 437 mPa·s at a shear rate of 1000 (1/s).Subsequently, drying was performed in a drying furnace set at 95° C. forabout 40 minutes to produce a second conductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(6) and (10)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymer (polymer (5)) with ahigher density. Hot-pressing was then performed at a pressingtemperature of 80° C. and a pressing pressure of 5.0 kN, for a pressingtime of 1 minute to produce the conductive porous layer of Example 12.

Example 13

Using the same material compositions of Example 12, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (6) and (10)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymer (polymer (5)) with a higher density. Hot-pressing wasthen performed at a pressing temperature of 90° C. and a pressingpressure of 10.0 kN, for a pressing time of 1 minute to produce theconductive porous layer of Example 13.

Example 14

(i) First Conductive Layer

Using the same material compositions of Example 12, the first conductivelayer-forming paste composition was prepared. The first conductivelayer-forming paste composition was applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm using anapplicator.

(ii) Second Conductive Layer

Polymer (7) was added to MEK, and the mixture was maintained using astirrer (media rotation speed: 300 rpm) at 80° C. for 60 minutes,thereby obtaining a PVDF solution having a solids content (polymer (7))of 5 wt % in which polymer (7) was dissolved in the MEK. Conductivecarbon fibers (4) (100 parts by weight), the prepared PVDF solution (200parts by weight (solids content: 10 parts by weight)), and methyl ethylketone (50 parts by weight) were subjected to media dispersion toprepare a second conductive layer-forming paste composition. The secondconductive layer-forming paste composition was applied on a PET film, onwhich a release layer had been formed, to a thickness of about 150 μmusing an applicator. Regarding the viscosity of the paste composition,the shear viscosity was about 366 mPa·s at a shear rate of 1000 (1/s).Subsequently, drying was performed in a drying furnace set at 95° C. forabout 40 minutes to produce a second conductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(6) and (10)) with a higher density was disposed adjacent to the surfaceof the second conductive layer having the polymer (polymer (7)) with ahigher density. Hot-pressing was then performed at a pressingtemperature of 90° C. and a pressing pressure of 10.0 kN, for a pressingtime of 1 minute to produce the conductive porous layer of Example 14.

Example 15

(i) First Conductive Layer

Polymer (5) was added to MEK, and the mixture was maintained using astirrer (media rotation speed: 300 rpm) at 80° C. for 60 minutes,thereby obtaining a PVDF solution having a solids content (polymer (5))of 10 wt % in which polymer (5) was dissolved in the MEK. Subsequently,conductive carbon particles (1) (100 parts by weight), polymer (10) (50parts by weight), the prepared PVDF solution (500 parts by weight(solids content: 50 parts by weight)), polymer (8) (100 parts by weight(solids content: 70 parts by weight)), and methyl ethyl ketone (1000parts by weight) were subjected to media dispersion to prepare a firstconductive layer-forming paste composition. The first conductivelayer-forming paste composition was applied on apolyethyleneterephthalate (PET) film, on which a release layer had beenformed, to a thickness of about 50 μm using an applicator. Regarding theviscosity of the paste composition, the shear viscosity was about 166mPa·s at a shear rate of 1000 (1/s). Subsequently, drying was performedin a drying furnace set at 95° C. for about 15 minutes to produce afirst conductive layer.

(ii) Second Conductive Layer

Conductive carbon fibers (4) (100 parts by weight), the PVDF solutionprepared in the same manner as in the first conductive layer above (100parts by weight (solids content: 10 parts by weight), polymer (8) (20parts by weight (solids content: 14 parts by weight)), and methyl ethylketone (200 parts by weight) were subjected to media dispersion toprepare a second conductive layer-forming paste composition. The secondconductive layer-forming paste composition was applied on a PET film, onwhich a release layer had been formed, to a thickness of about 150 μmusing an applicator. Regarding the viscosity of the paste composition,the shear viscosity was about 264 mPa·s at a shear rate of 1000 (1/s).Subsequently, drying was performed in a drying furnace set at 95° C. forabout 40 minutes to produce a second conductive layer.

(iii) Conductive Porous Layer

The first conductive layer and the second conductive layer were eachindividually detached from the PET film including the release layer, andthe surface of the first conductive layer having the polymers (polymers(5), (8), and (10)) with a higher density was disposed adjacent to thesurface of the second conductive layer having the polymers (polymers (5)and (8)) with a higher density. Hot-pressing was then performed at apressing temperature of 135° C. and a pressing pressure of 7.5 kN, for apressing time of 2 minutes to produce the conductive porous layer ofExample 15.

Comparative Example 1

Using the same material compositions of Example 1, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (9)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a lower density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Comparative Example 1.

Comparative Example 2

Using the same material compositions of Example 4, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (1) and (3)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymers (polymers (1) and (2)) with a lower density.Hot-pressing was then performed at a pressing temperature of 100° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Comparative Example 2.

Comparative Example 3

Using the same material compositions of Example 7, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymer (polymer (4)) with a lower density was disposedadjacent to the surface of the second conductive layer having thepolymer (polymer (5)) with a lower density. Hot-pressing was thenperformed at a pressing temperature of 100° C. and a pressing pressureof 7.5 kN, for a pressing time of 2 minutes to produce the conductiveporous layer of Comparative Example 3.

Comparative Example 4

Using the same material compositions of Example 11, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymer (polymer (5)) with a lower density was disposedadjacent to the surface of the second conductive layer having thepolymer (polymer (5)) with a lower density. Hot-pressing was thenperformed at a pressing temperature of 135° C. and a pressing pressureof 7.5 kN, for a pressing time of 2 minutes to produce the conductiveporous layer of Comparative Example 4.

Comparative Example 5

Using the same material compositions of Example 12, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (6) and (10)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymer (polymer (5)) with a lower density. Hot-pressing wasthen performed at a pressing temperature of 90° C. and a pressingpressure of 10.0 kN, for a pressing time of 1 minute to produce theconductive porous layer of Comparative Example 5.

Comparative Example 6

Using the same material compositions of Example 14, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (6) and (10)) with a lower densitywas disposed adjacent to the surface of the second conductive layerhaving the polymer (polymer (7)) with a lower density. Hot-pressing wasthen performed at a pressing temperature of 90° C. and a pressingpressure of 10.0 kN, for a pressing time of 1 minute to produce theconductive porous layer of Comparative Example 6.

Comparative Example 7

Using the same material compositions of Example 15, the first conductivelayer-forming paste composition and the second conductive layer-formingpaste composition were prepared. The first conductive layer-formingpaste composition and the second conductive layer-forming pastecomposition were each individually applied on a PET film, on which arelease layer had been formed, to a thickness of about 50 μm (the firstconductive layer) and a thickness of about 150 μm (the second conductivelayer) using an applicator. The first conductive layer and the secondconductive layer were each individually detached from the PET filmincluding the release layer, and the surface of the first conductivelayer having the polymers (polymers (5), (8), and (10)) with a lowerdensity was disposed adjacent to the surface of the second conductivelayer having the polymers (polymers (5) and (8)) with a lower density.Hot-pressing was then performed at a pressing temperature of 135° C. anda pressing pressure of 7.5 kN, for a pressing time of 2 minutes toproduce the conductive porous layer of Comparative Example 7.

First Conductive Layer Evaluation Test

As typical examples, Table 1 shows the results of the front and backsurfaces of the first conductive layers of Examples 1 and 10, which wereobserved by energy dispersion X-ray fluorescence analysis. An EX-23000BU energy dispersion X-ray fluorescence analysis device produced by JEOLLtd. was used as an analysis device. The results confirmed that theproportion of each of the F and S elements contained in Nafion resin andPTFE resin was different between the front surface and the back surfaceof the first conductive layer; and both the PTFE resin and Nafion resinsegregated between the front surface and the back surface of the firstconductive layer. Compared to the results of Example 1, the results ofExample 10 showed a significant difference. Accordingly, it wasconfirmed that resin was more likely to segregate when the firstconductive layer-forming paste composition had a low viscosity. Similarresults were obtained in Examples 2 to 9 and 11 to 15. In Table 1, “PETfilm contact surface” means a surface that is in contact with the PETfilm before the PET film is detached from the first conductive layer,and “PET film non-contact surface” is a surface opposite to the PET filmcontact surface.

TABLE 1 Example 1 Example 10 PET film PET film non- PET film non- PETfilm Evaluation contact contact contact contact element surface surfacesurface surface C 61.32 58.85 62.53 57.72 N 18.81 16.36 18.89 15.98 O2.8 3.23 2.52 3.41 F 16.68 20.85 15.71 21.97 S 0.39 0.71 0.35 0.92Second Conductive Layer Evaluation Test

As a typical example, Table 2 shows the results of the front and backsurfaces of the second conductive layer of Example 14, which wereobserved by energy dispersion X-ray fluorescence analysis, as in thefirst conductive layer evaluation test described above. An EX-23000 BUenergy dispersion X-ray fluorescence analysis device produced by JEOLLtd. was used as an analysis device. The results confirmed that theproportion of F elements in PVDF was different between the front surfaceand the back surface of the second conductive layer; and PVDF segregatedbetween the front surface and the back surface of the second conductivelayer. In the second conductive layer of Example 14, the polymersignificantly segregated compared to the first conductive layers ofExamples 1 and 10, even though the viscosity was extremely high. This ispresumably because the size of the carbon material used in the secondconductive layer in Example 14 was larger than that of the firstconductive layers in Examples 1 and 10, thus resulting in a large porousdiameter, and the second conductive layer in Example 14 had a greaterthickness than that of the first conductive layers in Examples 1 and 10.Similar results were obtained in Examples 1 to 13 and 15. In Table 2,“PET film contact surface” means a surface that is in contact with thePET film before the PET film is detached from the first conductivelayer, and “PET film non-contact surface” is a surface opposite to thePET film contact surface.

TABLE 2 Example 14 PET film non- PET film Evaluation contact contactelement surface surface C 69.66 66.67 N 28.45 22.49 O 1.14 0.42 F 0.6810.39 S 0.07 0.09Conductive Porous Layer Evaluation Test

Using a medium-temperature press device (produced by Tester Sangyo Co.,Ltd.), adhesion between the first conductive layer and the secondconductive layer in each of the conductive porous layers of Examples 1to 15 and Comparative Examples 1 to 7 was measured.

Adhesion was subjectively evaluated as to whether the layers wereadhered together in a manner such that one layer was not detached fromanother layer. Specifically, adhesion was rated A or B.

A: Strongly adhered and difficult to detach layers with hands.

B: Easy to detach layers with hands, or no adhesion was observed. Table3 shows the results.

TABLE 3 Adhesion between the first conductive layer and the secondconductive layer Example 1 A Example 2 A Example 3 A Example 4 A Example5 A Example 6 A Example 7 A Example 8 A Example 9 A Example 10 A Example11 A Example 12 A Example 13 A Example 14 A Example 15 A Comp. Exam. 1 BComp. Exam. 2 B Comp. Exam. 3 B Comp. Exam. 4 B Comp. Exam. 5 B Comp.Exam. 6 B Comp. Exam. 7 B

To attain high adhesion between the first conductive layer and thesecond conductive layer, Examples 1 to 15 confirmed that at least one ofthe following conditions must be satisfied: (A) the polymer in the firstconductive layer was present with a high density at the surface incontact with the second conductive layer, and (B) the polymer in thesecond conductive layer was present with a high density at the surfacein contact with the first conductive layer.

The results confirmed that, by layering the first conductive layer andthe second conductive layer in a manner such that at least one of thefollowing conditions was satisfied: (A) the polymer in the firstconductive layer was present with a high density at the surface incontact with the second conductive layer, and (B) the polymer in thesecond conductive layer was present with a high density at the surfacein contact with the first conductive layer, the conductive porous layerin which the first conductive layer having a uniform film thickness wasformed on the second conductive layer can be produced.

The invention claimed is:
 1. A method for producing the conductiveporous layer for batteries comprising a laminate comprising a firstconductive layer and a second conductive layer, the first conductivelayer comprising at least a conductive carbon material and a polymer,and the second conductive layer comprising at least a conductive carbonmaterial and a polymer, and the conductive porous layer satisfying atleast one of the following conditions: (A) the polymer in the firstconductive layer is present with a higher density at the surface of thelayer in contact with the second conductive layer than at the surfacenot in contact with the second conductive layer, and (B) the polymer inthe second conductive layer is present with a higher density at thesurface of the layer in contact with the first conductive layer than atthe surface not in contact with the first conductive layer, the methodcomprising the steps of: (I) applying a first conductive layer-formingpaste composition to a substrate and drying, wherein the compositioncomprises at least a conductive carbon material and a polymer, and thendetaching the resulting first conductive layer from the substrate toproduce a first conductive layer having a polymer with a higher densityat one side surface than at the opposite side surface, (II) applying asecond conductive layer-forming paste composition to a substrate anddrying, wherein the composition comprises at least a conductive carbonmaterial and a polymer, and then detaching the resulting secondconductive layer from the substrate to produce a second conductive layerhaving a polymer with a higher density at one side surface than at theopposite side surface, and (III) disposing the first conductive layerand the second conductive layer in such a manner as to satisfy at leastone of the following conditions: (A) the polymer in the first conductivelayer is present with a higher density at the surface of the layer incontact with the second conductive layer than at the surface not incontact with the second conductive layer, and (B) the polymer in thesecond conductive layer is present with a higher density at the surfaceof the layer in contact with the first conductive layer than at thesurface not in contact with the first conductive layer; and performinghot-pressing for bonding.
 2. The method according to claim 1, whereinthe polymer in step (I) has a glass transition temperature of −100 to300° C.
 3. The method according to claim 1, wherein the polymer in step(II) has a glass transition temperature of −100 to 300° C.
 4. The methodaccording to claim 1, wherein step (III) is a step of disposing thefirst conductive layer and the second conductive layer in such a manneras to satisfy both of the conditions (A) and (B), and performinghot-pressing for bonding.
 5. The method according to claim 1, whereinthe conductive carbon material in step (II) is conductive carbon fiberswith an average fiber diameter of 5 μm or more and/or conductive carbonparticles with an average particle diameter of 5 μm or more.